‖Mon‐sieur″ (?), n.; pl.Messieurs (#). [F., fr. mon my + Sieur, abbrev. of seigneur lord. See Monseigneur.] 1. The common title of civility in France in speaking to, or of, a man; Mr. or Sir. [Represented by the abbreviation M. or Mons. in the singular, and by MM. or Messrs. in the plural.]
2. The oldest brother of the king of France.
3. A Frenchman. Shak.